Today I have to go to the library to take back a book.
I have nothing to say back to you.
"Could you return the cookies I gave you yesterday?" "Huh? You mean, I should throw them up?"
This word consists of kanji with hiragana attached. Because the hiragana ends with an う sound, you know this word is a verb. The kanji itself means return so the verb version means to return.
This is more like "to return a thing" rather than returning home, which would be 帰る, a word you haven't seen yet (but will soon, I'm sure!).
Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You didn't learn that reading with this kanji, so here's a mnemonic to help you:
You have to return the Car egg (かえ) you found on the side of the road. It will birth a little car, but it needs its mother. So, you try to figure out how to return it. Go ahead and think through that process in your mind. Also think about how weird a car egg would be.